Arkanaut:It makes things worse if it's not enforced. You need to make it clear that if the truce is broken, whichever side breaks it gets punished.

Who does the punishing? A foreign government? And just how much power would this government wield over the belligerents? Can they do that forever? What Leviathan are you talking about? If a government has the strength to indefinitely keep two squabbling states from warring without resolving their dispute, then said government is pretty much their ruler rather than their mediator.